1. Field of the Invention
The present invention relates to a heat storage material comprising CaCl.sub.2 hydrate for heat storage and radiation with a latent heat in a phase change of fusion and solidification. The heat storage material is used for an air-conditioning, a waste heat recovery or a solar heat storage.
2. Description of the Prior Art
It is most important for the latent heat storage material to be always stable in the repeating heat storage and radiation.
CaCl.sub.2.6H.sub.2 O has been considered to be optimum, since it results in the phase change at 29.degree. C. and has a latent heat of 41 cal/g. and is economical. However, when CaCl.sub.2.6H.sub.2 O is repeatedly phase-changed, a crystallization of CaCl.sub.2.4H.sub.2 O (.alpha.-phase: melting point of 45.degree. C.; .gamma.-phase: melting point of 38.degree. C.) is easily caused. The .alpha.-phase having a high melting point is usually found. When such crystallization is caused, the crystal precipitates at the bottom of the fused liquid. Thus, the phase change to CaCl.sub.2.6H.sub.2 O is not attained in the solidification. It is necessary to prevent the crystallization of CaCl.sub.2.4H.sub.2 O in order to use CaCl.sub.2.6H.sub.2 O as the heat storage material.
In order to overcome the above-mentioned disadvantages,
(a) the maximum temperature in the heating step is given to about 50.degree. C. so as to melt CaCl.sub.2.4H.sub.2 O or
(b) a small amount of SrCl.sub.2.6H.sub.2 O is added to shift the peritectic composition to the side of CaCl.sub.2.6H.sub.2 O or
(c) a large amount of water is added.
As a reference, the relation of the region of crystallization of CaCl.sub.2.4H.sub.2 O and the phase is shown in FIG. 1 wherein a concentration of CaCl.sub.2 (wt.%) is plotted on the abscissa and a temperature is plotted on the ordinate and the references x, .DELTA. and .cndot. respectively designate the conditions of the temperature and the concentration for resulting in the growth of .alpha.-phase, .beta.-phase or .gamma.-phase of CaCl.sub.2.4H.sub.2 O. The binary phase diagram of CaCl.sub.2 -H.sub.2 O is referred to B. Bergthorsson; Acta Chem. Scand 26 (1973) No. 3, 1292.
The following disadvantages are found as the proposals for preventing the crystallization of CaCl.sub.2.4H.sub.2 O.
With regard to the proposal (a), the application is remarkably limited. With regard to the proposal (b), only tests are carried out but the practical application is not attained. Sometimes, the addition of the second component causes the crystallization of CaCl.sub.2.4H.sub.2 O. With regard to the proposal (c), a heat of fusion is remarkably reduced to be 30 cal/g. or lower.